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Aviation History
1910
1910 - 0495.PDF
JUNE 25, 1910. 1/yGHf] CORRESPONDENCE. *#* The name and addre s cj the writer (not necessarily for publication) MUST in all cases accompany letters intended for insertion, or containing queries. Correspondents asking questions relating to articles which they have read in FLIGHT, would much facilitate our work of reference by giving the number of the letter. NOTE.—Owing to the great mass of valuable and interesting corre spondence which we receive, immediate publication is impossible, but each letter will appear practically in sequence and at the earliest possible moment. THE i DUNNE AEROPLANE CONTROL. ([576] In considering the control of our machine, it is essential to remember that the wing tips are not normally inclined at a positive angle to the trajectory, as is the case in every other machine. Actually they are at a negative angle. IP When we want to steer to the right we pull back the right-hand lever, thereby elevating the trailing edge of the right-hand flap. In an ordinary system, regarding the tip as normally positively inclined, you would say, " The angle of incidence of the right-hand extremity is thereby reduced." This is incorrect. The angle of incidence, which is negative is thereby increased, and the drift, one might almost call it the negative drift, is increased. This wing, therefore, 'tends to hang back, at the same time, owing to the increased negative inclination, this side is depressed. One could steer by this movement alone, were it not that the flap, situated behind the •centre of gravity, is an elevator, and when it depresses the right wing tip it depresses the rear of the machine as a whole. In order •to counteract this elevator effect, we simultaneously push forward the left-hand lever, thereby lowering the trailing edge of the left- tiand flap. This does not "increase" the angle of incidence on that side, but decreases the previous negative angle of incidence of ithat side. This left side then has more lift than it had before, and 'balances the elevator effect of the right-hand flap. At the same 'time, owing to the decrement in the negative angle, this left tip has less resistance than formerly, and so travels taster than before, thus aiding the turning movement slightly. Since the right tip is •depressrd and the left tip raised, the machine is banked with the right side lower than the left. Possibly some may imagine that this banking is the reverse of that usually done in rounding a corner with an aeroplane, as there appears to be some confusion in aeronautical literature on this point. Most people seem to argue that when a machine is circling to the right, the left side, which travels faster than the other, rises, tending to capsize the machine, and that ailerons or warping have to be used to keep the right side up. The problem is really a purely •quantitative one. The effect of any rudder action is primarily to point themachine's head in the newdirection. Then you have the cen trifugal tendency of a machine of, in our case, 1.700 lbs. to contend with. Is the banking which occurs owing to the outer wing moving faster than the inner sufficient to overcome centrifugal movement (which is of course a sort of side-slip) or not? The answer obviously depends on the mass, the speed, the radius of the circle, and the design of the machine. In a machine with a big dihedral surface forward, like the Antoinette, or big vertical surfaces well forward and above the centre of gravity like the Voisin, the centri fugal motion, which occurs as soon as the bow is diverted from its previous course, produces reactions on the underside ol the dihedral wing, or on the vertical panels, tending to cant up the outer side considerably, quite apart from the lift it might get owing to its relatively faster movement. In our own machine the immediate effect of this centrifugal side-slip would be to depress the outer wing. You will see this if you look at the machine from the side in one of your photographs. Thus : the machine is turning to the right, and the centrifugal movement, which we are assuming for the moment to be unbalanced, causes it to skid to the left. The rough sketch above shows the position, the machine skidding towards the spectator. Notice that the left-hand surfaces appear as a com paratively thin edge, while a very broad expanse of the under surfaces of the right-hand sicje is exposed. The right-hand side is thus lifted and the left depressed. This is more than sufficient to counteract the tendency of the left to rise owing to its relatively faster motion. Therefore our controls are arranged so as to cause the outer side to rise and the inner side to fall. As a matter of fact this machine can bank up on a sharp turn to over 450 without any centripetal movement being apparent. J. W. DUNNE. [The above very lucid explanation of the steering of the Dunne aeroplane was sent in reply to an editorial letter on the subject, and as we feel that our readers would prefer to have Lieut. Dunne's description in his own words, we are publishing the letter itself simultaneously with our article on the machine.—ED.] SINGLE^SURFACED PLANES. [577] AV Mr. S. A. Hall's letter, No. 490, in your issue of April 30th. I am inclined to argue in favour of leaving the ribs of a single-surfaced plane exposed on the under side, as any resistance on the upper suiface of a plane would lessen its rising effect. I have found from experiment that slight irregularities on the under surface tend, if anything, to increase the lift. Mitcham. G. R. BRAGG SMITH. A BLE'RIOT IN NORTH WALES. [S78] I enclose some photographs of my Bleriit monoplane, and as I claim to be the first one to fly on an aeroplane in North Wales I thought they would be interesting to your valuable paper. I have been practising for some time on my machine, and had rather a nasty smash about two months ago, landing in the railway hedge from a height of about 30 feet. However, on the 26th of May I towed my machine to a large field, and succeeded in making a flight of half a mile, during which I attained a height of about 70 feet. The centre photograph shows the method of towing the Bleriot behind my car. In the left-hand picture I am starting up prior to my flight, and that on the right was taken by my mechanic immediately after landing. The Bleriot behaved very well during the flight, at the end of which I switched off and glided down, and, although it bumped a little on landing, nothing was damaged. Since then I have made numerous small flights, and hope to do better when I become more accustomed to the machine. Bodfari, North Wales. VIVIAN V. D. HEWITT. Mr. Vivian V. D. Hewitt's Bleriot. 493
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